Method for producing nickel powder

ABSTRACT

Provided is a method for producing nickel powder, wherein fine nickel powder serving as seed crystals needed for production of nickel powder is produced from a solution containing a nickel ammine sulfate complex according to the amount needed for the production of the nickel powder. The method for producing nickel powder is characterized in that: the solution containing the nickel ammine sulfate complex, an insoluble solid, and a dispersant are continuously fed into a reaction vessel, followed by stirring to prepare a solution containing a nickel complex ion; hydrogen gas is blown into the prepared solution to reduce the nickel complex ion in the solution containing the nickel complex ion, thereby forming a precipitate of nickel particles on the surface of the insoluble solid; and thereafter the post-reduction solution is extracted from the reaction vessel.

BACKGROUND Field of the Invention

The present invention relates to a method for producing fine nickelpowder available as seed crystals from a solution containing a nickelammine sulfate complex, and the invention can be applied, in particular,in a treatment for controlling the number of nickel powder generated torequirement.

Related Art

Methods for producing fine nickel powder have been known includingatomization methods of dispersing molten nickel in gas or water toobtain fine powder, and dry processes, such as CVD processes, ofvolatilizing nickel, and reducing the nickel in a gaseous phase toobtain nickel powder as described in Japanese Patent ApplicationLaid-Open No. 2005-505695.

Methods for producing nickel powder by a wet process have been knownincluding a method of producing nickel powder using a reducing agent asdescribed in Japanese Patent Application Laid-Open No. 2010-242143, andan atomization thermal decomposition method of atomizing a nickelsolution in a reduction atmosphere at a high temperature to obtainnickel powder through a thermal decomposition reaction as described inJapanese Patent No. 4286220. However, these methods are not economicalbecause these methods require expensive reagents and a large amount ofenergy.

In contrast, a method as described in “The Manufacture and properties ofmetal powder produced by the gaseous reduction of aqueous solutions”,Powder metallurgy, No. 1/2 (1958), 40-52 is industrially inexpensive anduseful, in which hydrogen gas is fed to a nickel ammine sulfate complexsolution to reduce nickel ions in the complex solution, obtaining nickelpowder. However, this method tends to produce coarse particles of thenickel powder, and has difficulties in producing a fine powder which canbe used as seed crystals.

When particles are produced from an aqueous solution and are grown, asmall amount of fine crystals called seed crystals is added, and areducing agent is fed thereto to grow the seed crystals into a powderhaving a predetermined particle size.

The seed crystals used in this method are often obtained throughpulverization of a product, which requires labor, reduces the yield, andthus increases cost. In addition, the pulverization does not necessarilyproduce seed crystals having an optimal particle size or optimalproperties.

Furthermore, an appropriate amount of seed crystals is always requiredto stably advance the operation to produce nickel powder. On the otherhand, preparation of excess seed crystals increases stock in progressand the labor for management thereof, thus reducing the productionefficiency.

As described above, a method for stably obtaining an amount of seedcrystals needed for the actual operation has been demanded.

Accordingly, an object of the present invention is to provide a methodfor producing nickel powder, wherein fine nickel powder serving as seedcrystals required for production of nickel powder is produced from asolution containing a nickel ammine sulfate complex according to theamount needed for the production of the nickel powder.

SUMMARY

A first aspect of the present invention relates to a method forproducing nickel powder, wherein: a solution containing a nickel amminesulfate complex, an insoluble solid, and a dispersant are continuouslyfed into a reaction vessel, followed by stirring to prepare a solutioncontaining a nickel complex ion; hydrogen gas is blown into the preparedsolution to reduce the nickel complex ion in the solution containing thenickel complex ion, thereby forming a composite including a precipitateof nickel particles on a surface of the insoluble solid, to therebyprepare a reduced slurry containing the composite; and thereafter, whenthe reduced slurry is extracted from the reaction vessel, a feed amountof the solution containing the nickel ammine sulfate complex, theinsoluble solid, and the dispersant and a discharge amount of thereduced slurry are adjusted to keep a constant amount of the solution inthe reaction vessel.

The present invention also relates to a method for producing nickelpowder, wherein the amount of the dispersant to be added in the firstaspect is controlled to control the number of nickel powder obtainedthrough the formation of the precipitate of nickel in the reduction.

The present invention further relates to a method for producing nickelpowder, wherein the dispersant in the first and eighth aspects is apolyacrylate and the amount of the dispersant to be added is in anamount of more than 1.0% by weight and 10.0% by weight or less based ona weight of the insoluble solid in the reaction vessel.

The present invention additionally relates to a method for producingnickel powder, wherein the dispersant in the first and eighth aspects isa lignosulfonic acid and the amount of the dispersant to be added is inan amount of more than 2.0% by weight and 20.0% by weight or less basedon a weight of the insoluble solid in the reaction vessel.

The present invention can provide a method for economically andefficiently producing fine nickel powder, which is optimal as the seedcrystals used in production of nickel powder, from a nickel amminesulfate complex solution through reduction and precipitation usinghydrogen gas according to the amount needed, and which exhibits aremarkable industrial effect.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 This is a production flowchart in a method for producing nickelpowder according to the present invention, in which a dispersant and aninsoluble solid are added.

FIG. 2 This is a graph illustrating a change in the concentration ofnickel in the solution after the reaction in Reference Examples 1 to 4where sodium polyacrylate is used.

FIG. 3 This is a graph illustrating a change in the concentration ofnickel in the slurry of Reference Comparative Example 2 (dispersant isnot added) plotted against the reaction time, where the change is causedby the concentration of the dispersant during the reduction withhydrogen.

FIG. 4 This is a graph illustrating the relation between the number ofnickel powder and the amount of sodium polyacrylate added according toReference Example 5.

FIG. 5 This is a graph illustrating the relation between the number ofnickel powder and the amount of sodium lignosulfonate added according toReference Example 6.

FIG. 6 This is a graph illustrating the comparison in particle sizedistribution between the insoluble solid (nickel powder) as seedcrystals and the produced nickel powder according to Example 7.

DETAILED DESCRIPTION

The present invention is a method for producing nickel powder by addinga dispersant and an insoluble solid as seed crystals to a nickel amminesulfate complex solution, and blowing hydrogen gas thereinto, wherein atarget amount of fine nickel powder is produced through control of theamount of dispersant to be added.

Hereinafter, the method for producing nickel powder according to thepresent invention will be described with reference to the productionflowchart in FIG. 1.

[Nickel Ammine Sulfate Complex Solution]

A nickel ammine sulfate complex solution that can be used in the presentinvention is not particularly limited, but it is suitable to use anickel ammine sulfate complex solution obtained by dissolving anickel-containing material, such as an industrial intermediate includingone or a mixture of two or more selected from nickel and cobalt mixedsulfide, crude nickel sulfate, nickel oxide, nickel hydroxide, nickelcarbonate, and nickel powder, with sulfuric acid or ammonia depending onthe components to prepare a nickel-containing leachate (solutioncontaining nickel), subjecting the nickel-containing leachate to aliquid-purification step such as solvent extraction, ion exchange, orneutralization to remove impurity elements in the solution, and addingammonia to the resulting solution.

[Mixing Step]

In this step, first, a dispersant is added to the nickel ammine sulfatecomplex solution.

Any polyacrylate or lignosulfonate dispersant can be used in this stepwithout particular limitation. Among those industrially available at lowcost, suitable polyacrylates are calcium polyacrylate, sodiumpolyacrylate and potassium polyacrylate, and suitable lignosulfonatesare calcium lignosulfonate, sodium lignosulfonate, and potassiumlignosulfonate.

The concentration of ammonium sulfate in the solution is preferably inthe range of 10 to 500 g/L in conjunction with the production methodillustrated in FIG. 1. A concentration of more than 500 g/L is beyondthe solubility, precipitating crystals. A concentration of less than 10g/L is difficult to achieve because ammonium sulfate is newly generatedby the reaction.

<Addition of Insoluble Solid>

In the production method according to the present invention illustratedin FIG. 1, in the next step, an insoluble solid, which is at leastinsoluble in the nickel ammine sulfate complex solution having anadjusted concentration of the dispersant and serves as a matrix for aprecipitate, is added to the complex solution.

Any insoluble solid having low solubility to the nickel ammine sulfatecomplex solution, an ammonium sulfate aqueous solution, or an alkalisolution can be added here without particular limitation. For example,nickel powder, iron powder, alumina powder, zirconia powder, or silicapowder can be used.

Unlike the conventional methods generally used in which powder isprecipitated using seed crystals to make it into a product containingthe seed crystals, in the present invention, after the necessaryprecipitation of particles onto the surface of the insoluble solid iscompleted, the insoluble solid is separated from the yielded and grownprecipitate, and only the powder of the separated precipitate isextracted as a product. Such a method in the present invention isintended to avoid the influences of impurities in the seed crystalsitself over the product.

Any amount of insoluble solid can be added without particularlimitation. The amount thereof is selected according to the type of thesolid such that the insoluble solid can be mixed with the nickel amminesulfate complex solution through stirring. As one example, an amount ofabout 50 to 100 g/L may be added.

The insoluble solid can also have any shape and size without particularlimitation. Suitable are those having strength to stand impact orfriction and having a smooth surface so as to effectively separate thenickel precipitate, because the nickel precipitates on the surface ofthe insoluble solids may be separated through application of collisionor vibration as described later.

Considering the effective separation of the insoluble solid from thenickel precipitate on the surface thereof, the insoluble solid suitablyused in the actual operation has a rounded shape such as a spherical orelliptical shape and has a diameter of about 0.05 to 3 mm. Preferably,the insoluble solid according to the present invention is used afteradhering substances to the surface of the insoluble solid are removedthrough the application of collision or impact to the insoluble solidprior to the precipitation of nickel.

Furthermore, the insoluble solid after the separation of the nickelprecipitate can be subjected to a pre-treatment such as washing, whennecessary, and can be repeatedly used.

<Addition of Dispersant>

The present invention is characterized in that the insoluble solid isused as seed crystals, and the dispersant is added. The dispersant cansufficiently disperse the added insoluble solid in a complex solution togenerate a fine nickel precipitate on the surface of the insolublesolid. The dispersant is added desirably in an appropriate amount in therange of 1.0 to 20.0% by weight of the weight of the insoluble solidadded to the complex solution. In particular, a polyacrylate and alignosulfonate are preferred.

1. Case where a Polyacrylate is Used as Dispersant

In the case where the insoluble solid is used as seed crystals and apolyacrylate is used as a dispersant (production method illustrated inthe production flowchart in FIG. 1), the amount of the dispersant to beadded is more than 1.0% by weight and 10.0% by weight or less based onthe weight of the insoluble solid added to the slurry, and desirably2.0% by weight or more and 6.0% by weight or less.

At an addition amount of 1.0% by weight or less, the nickel powder doesnot precipitate. An amount of 2.0% by weight or more is preferredbecause the insoluble solid can be sufficiently dispersed to control thenumber of generated nickel powder proportionately with the amount of thedispersant added.

In contrast, the seed crystals tend to be increased even if the upperlimit of the amount of the dispersant is beyond 6.0% by weight. Anexcess large number of seed crystals generated causes handlingdifficulties and aggregation between the dispersants. Considering theeffect commensurate with the amount of the dispersant added, such anupper limit is not preferred. Accordingly, the upper limit is 10.0% byweight or less, more preferably 6.0% by weight or less.

2. Case where a Lignosulfonate is Used as Dispersant

In the case where a lignosulfonate is used as a dispersant (productionmethod illustrated in the production flowchart in FIG. 1), the amount ofthe dispersant to be added is 2.0% by weight or more and 20.0% by weightor less based on the weight of the insoluble solid added to the slurry.An amount of 2.0% by weight or less cannot yield nickel powder, so thatthe amount of the dispersant is required to be more than 2.0% by weight.In particular, an amount of more than 5.0% by weight is preferredbecause the number of nickel powder generated can be controlledproportionately with the amount of the dispersant added.

[Reduction and Precipitation Step]

Next, the nickel complex ion in the slurry is reduced with hydrogen toform a composite including the insoluble solid and a nickel precipitateon the surface thereof. This “reduction and precipitation step” can beperformed in a batch manner and a continuous manner.

First, in the “reduction and precipitation step” where the reduction andthe precipitation are performed in batch, a slurry formed of adispersant and an insoluble solid added is charged into a reactionvessel in a container resistant to high pressure and high temperature.Hydrogen gas is blown into the slurry contained in the reaction vesselof the container resistant to high pressure and high temperature toreduce the nickel complex ion in the slurry, thereby forming a reducedslurry containing a composite including the insoluble solid contained inthe slurry and nickel generated as a precipitate on the surface thereof.

At this time, the reaction temperature is preferably in the range of 150to 200° C. A reaction temperature of less than 150° C. reduces thereduction efficiency. A reaction temperature of higher than 200° C. hasno influences over the reaction; rather, such a temperature is notsuitable because it increases loss of thermal energy.

Furthermore, the pressure during the reaction is preferably 1.0 to 4.0MPa. A pressure of less than 1.0 MPa reduces the reaction efficiency. Apressure of more than 4.0 MPa has no influences over the reaction;rather, it increases loss of hydrogen gas.

Next, the slurry formed of the dispersant and the insoluble solid addedis continuously fed into a reaction vessel of a container resistant tohigh pressure and high temperature, and hydrogen gas is continuouslyblown into the slurry flowing in the reaction vessel to reduce nickelcomplex ion in the slurry. Thereby, a reduced slurry containing acomposite including the insoluble solid and a nickel precipitate formedon the surface thereof is obtained. After the reduction reaction togenerate the nickel precipitate, the resulting reduced slurry iscontinuously extracted and recovered from the reaction vessel, and isfed to the subsequent step.

In other words, by performing the reduction reaction by such acontinuous step, the time required to replace the slurry or set theconditions for the reduction treatment can be reduced, and animprovement in production efficiency can be expected. Control of theflow rate of the slurry enables the adjustment of the amount ofproduction, resulting in a reduction in size of the reaction vessel andeconomical advantages such as a reduction in capital investment andrepairs of facilities.

In such a reduction and precipitation step, the reaction temperature ispreferably in the range of 150 to 200° C. A reaction temperature of lessthan 150° C. reduces the reduction efficiency. A reaction temperature ofhigher than 200° C. has no influences over the reaction; rather, it isnot suitable because it increases loss of the thermal energy.

Furthermore, a pressure of 1.0 to 4.0 MPa is preferably applied to agaseous phase portion in the reaction vessel during the reaction. Apressure of less than 1.0 MPa reduces the reaction efficiency. Apressure of more than 4.0 MPa has no influences over the reaction;rather, it increases loss of hydrogen gas.

Because of the effect of the dispersant in the reduction andprecipitation treatment according to the present invention, theinsoluble solid can be sufficiently dispersed in the slurry. In such astate, a nickel precipitate in the form of a finely powdery precipitatecan be formed on the surface of the insoluble solid. Nickel can beextracted and recovered from the nickel ammine sulfate complex solution.Furthermore, the amount of nickel powder generated through precipitationcan also be adjusted through the adjustment of the amount of thedispersant to be added.

[Separation Step]

This step is performed when the insoluble solid is used. In this case,the nickel precipitate generated in the reduction and precipitation stepadheres to the surface of the insoluble solid, and cannot be used insuch a state. For this reason, the nickel precipitate formed on thesurface of the insoluble solid is separated from the insoluble solid,and is recovered.

Examples of specific separation methods include a method of placing aninsoluble solid and a nickel precipitate into water to avoid oxidationdue to heat generated, colliding the insoluble solids each other underrotating to separate the nickel precipitate from the surface of theinsoluble solid, and sieving the nickel precipitate to obtain nickelpowder; a method of rotating a nickel precipitate on a wet sieve, andsimultaneously sieving the separated nickel precipitate to obtain nickelpowder; or a method of separating a solution through ultrasonicvibration, and sieving the resulting nickel precipitate to obtain nickelpowder. Any sieve having an opening smaller than the insoluble solid canbe used in the sieving step.

The nickel powder thus produced can be used in application to nickelpastes as an inner constitutional substance of stacked ceramiccapacitors, for example. Besides, high purity nickel metal can beproduced through repetition of the reduction with hydrogen using therecovered nickel powder as seed crystals to grow particles.

EXAMPLES

Hereinafter, the present invention will be described by way of Examplesand Reference Examples.

Reference Example 1 [Mixing Step]

336 g of nickel sulfate hexahydrate, which amount is equivalent to 75 gof nickel content, 330 g of ammonium sulfate, and 191 ml of 25% aqueousammonia were added to prepare a nickel ammine sulfate complex solution.According to the production flow in FIG. 1, first, 75 g of nickel powderhaving an average particle size (D50) of 85 μm as an insoluble solidserving as a precipitation matrix for seed crystals, and sodiumpolyacrylate having a molecular weight of 4000 as a dispersant in anamount of 1.5 g was added, which was equivalent to 2% by weight of theweight of the insoluble solid serving as seed crystals. Pure water wasadded so that the volume of the solution was adjusted to 1000 ml.Thereby, a slurry was formed.

[Reduction and Precipitation Step]

The resulting slurry was then placed into an internal cylindrical can ofan autoclave. The slurry was heated to 185° C. with stirring. While thetemperature was maintained, hydrogen gas was blown and fed into theslurry from a hydrogen tank so that the pressure in the autoclave became3.5 MPa.

A sample of reduced slurry was extracted from the sample outlet of theautoclave every two minutes after the start of feed of hydrogen gas, andwas subjected to solid liquid separation. The concentration of nickel inthe filtrate was analyzed.

As the reaction progresses, nickel is precipitated as powder, and inturn, the concentration of nickel in the filtrate is reduced by theamount of the nickel precipitate. As shown in FIG. 2, from thecalculation of a change in the concentration of nickel, 80% or more ofnickel could be reduced and recovered in 30 minutes.

After the lapse of 30 minutes from the start of feeding hydrogen gas,the feed of hydrogen gas was stopped, and the internal cylindrical canwas cooled. After the cooling, the slurry in the internal cylindricalcan was filtered to recover 42.7 g of precipitated nickel powder.

The recovered nickel powder was observed. It was confirmed that finenickel powder usable as seed crystals was generated.

Reference Example 2

Nickel powder was produced, and was recovered by the same method andconditions as in Reference Example 1 except that 4.5 g of sodiumpolyacrylate, which amount is equivalent to 6% by weight of the weightof the seed crystals, was added.

The results are shown in FIG. 2. As shown in FIG. 2, 80% or more ofnickel could be reduced and recovered in 30 minutes as in ReferenceExample 1.

Reference Example 3

Nickel powder was produced, and was recovered by the same method andconditions as those in Reference Example 1 except that 7.5 g of sodiumpolyacrylate, which amount is equivalent to 10% by weight of the weightof the seed crystals, was added.

The results are shown in FIG. 2. As shown in FIG. 2, 80% or more ofnickel could be reduced and recovered in 30 minutes as in ReferenceExample 1.

Reference Example 4

Nickel powder was produced, and was recovered by the same method andconditions as in Reference Example 1 except that 0.75 g of sodiumpolyacrylate, which amount is equivalent to 1% by weight of the weightof the seed crystals, was added.

The results are shown in FIG. 2. As shown in FIG. 2, from thecalculation of a change in the concentration of nickel, about 50% ofnickel could be reduced and recovered in 30 minutes.

Reference Comparative Example 1

Nickel powder was prepared with the same solution composition andreduction conditions as in Reference Example 1 except that thedispersant and the insoluble solid were not added.

The concentration of nickel in the sampled solution was reduced from 75g/L to about 45 g/L. Any nickel powder could not be recovered from thesolution after the blowing of hydrogen gas was completed. It wasconfirmed that scaling of plate-like nickel was generated at the sidewalls inside the internal cylindrical can and the stirrer.

Reference Comparative Example 2

Nickel powder was produced by the same method as in Reference Example 1except that the dispersant was not added and 75 g of nickel powder as aninsoluble solid was added.

The results are shown in FIG. 3. As shown in FIG. 3, from thecalculation of a change in the concentration of nickel, only about 20%of nickel could be recovered in 30 minutes.

Reference Example 5

191 ml of 25% aqueous ammonia was added to a solution containing 336 gof nickel sulfate hexahydrate, which amount is equivalent to 75 g ofnickel, and 330 g of ammonium sulfate to prepare a nickel ammine sulfatecomplex solution. Furthermore, according to the production flowillustrated in FIG. 1, a solution of sodium polyacrylate having amolecular weight of 4000 and a concentration of 40% was added in anamount of 0.38 g, 1.88 g, 3.75 g, 7.5 g, and 11.3 g to the resultingnickel ammine sulfate complex solution, respectively, and the totalvolume of the solutions was adjusted to 1000 ml. Thereby, five solutionswere prepared.

75 g of nickel powder having an average particle size (D50) of 85 μm asan insoluble solid serving as the precipitation matrix was added to eachof the resulting solutions to prepare a desired slurry. The net amountsof the sodium polyacrylate added here were equivalent to 0.2% by weight,1.0% by weight, 2.0% by weight, 4.0% by weight, and 6.0% by weight,respectively, based on the amount of the insoluble solid.

The resulting mixture slurries were placed into an internal cylindricalcan of an autoclave. Each slurry was heated to and held at 185° C. withstirring. In this state, hydrogen gas was blown and fed into the slurryso that the pressure in the autoclave became 3.5 MPa. After the lapse of60 minutes from the start of feeding hydrogen gas, the feed of hydrogengas was stopped, and the internal cylindrical can was cooled.

[Separation Step]

After the cooling, the slurry in the internal cylindrical can wasfiltered to recover a composite of the insoluble solid and a nickelprecipitate. The insoluble solid as the matrix and the nickelprecipitate on the surface of the insoluble solid were separated undervibration using a wet sieve having an opening of 75 μm to recover nickelpowder.

The particle size of the recovered nickel powder under the sieve wasmeasured with a particle size distribution analyzer (made by Microtrac,Inc., trade name 9320-X100 type) to determine the particle sizedistribution.

Assuming that the recovered nickel powder was a true sphere, using thedetermined average particle size: D and the nickel density: p=8.9 g/cm³,the number of recovered nickel powder was calculated from Expression(1):

[Expression 1]

The Number of nickel powder=(Mass of recovered nickelpowder)/[8.9×4π×(D/2)³/3]  (1)

The relation between the number of nickel powder calculated fromExpression (1) and the amount of sodium polyacrylate added is shown inFIG. 4.

From FIG. 4, it is found that there is a correlation between the amountof sodium polyacrylate added and the number of nickel powder, and thatthe amount of nickel powder generated can be adjusted by the amount ofsodium polyacrylate added. In particular, it is found that an amount ofadded sodium polyacrylate of 1.0% by weight or less cannot yield nickelpowder, and an amount of more than 1.0% by weight can control the numberof generated nickel powder proportionately with the amount of sodiumpolyacrylate added.

Reference Example 6

Nickel powder was produced by the same method as in Reference Example 1except that sodium lignosulfonate was used as a dispersant in amounts of1.5 g, 3.0 g, 4.5 g, 7.5 g, 11.3 g, and 15.0 g, respectively. Theamounts of insoluble solid of sodium lignosulfonate added are equivalentto 2.0% by weight, 4.0% by weight, 6.0% by weight, 10.0% by weight,15.0% by weight, and 20.0% by weight, respectively.

For the resulting nickel powder, the number of nickel powder wascalculated as in Reference Example 5 through calculation usingExpression (1).

The relation between the number of nickel powder calculated fromExpression (1) and the amount of sodium lignosulfonate added is shown inFIG. 5.

Example 7

Water and 3 g/l of sodium polyacrylate as a dispersant, which amount isequivalent to 2% by weight of the weight of an insoluble solid, wereadded to a nickel ammine sulfate complex solution containing 83 g/L ofnickel ions, 120 g/L of ammonium sulfate, and 182 g/L of 25% aqueousammonia and nickel powder having an average particle size (D50) of 90 μmas the insoluble solid to prepare a seed crystal slurry containingnickel powder having a concentration of 165 g/L.

The nickel ammine sulfate complex solution and the seed crystal slurryprepared above were then continuously fed to an autoclave using a pump.While the autoclave was held at 185° C. with stirring, hydrogen gas wasblown and fed into the slurry from a hydrogen tank so that the pressurein the cylindrical can of the autoclave became 3.5 MPa. At this time,after hydrogen gas was blown into the slurry, the slurry in theautoclave was stagnated for one hour. To keep a constant amount of thesolution in the autoclave, the feed and discharge amounts of the nickelammine sulfate complex solution and the seed crystal slurry wereadjusted, and the slurry after the reaction was continuously extractedand recovered from the autoclave.

The number of nickel powder was calculated through the calculation usingExpression (1) from the weight of the obtained nickel powder.

As a result, Table 1 shows that the number of particles increased, andthe particle size distribution in FIG. 6 shows that fine nickel powderwas produced.

TABLE 1 Seed Produced nickel crystals*¹ powder The number of nickelpowder 410 18000 [×10⁶ particles/L] *¹90 μm nickel powder

1. A method of producing nickel powder, wherein: a solution containing anickel ammine sulfate complex, an insoluble solid, and a dispersant arecontinuously fed into a reaction vessel, followed by stirring to preparea solution containing a nickel complex ion; hydrogen gas is blown intothe solution containing the nickel complex ion to reduce the nickelcomplex ion in the solution containing the nickel complex ion, therebyforming a composite including a precipitate of nickel particles on asurface of the insoluble solid, to thereby prepare a reduced slurrycontaining the composite; and thereafter, when the reduced slurry isextracted from the reaction vessel, a feed amount of the solutioncontaining the nickel ammine sulfate complex, the insoluble solid, andthe dispersant and a discharge amount of the reduced slurry are adjustedto keep a constant amount of the solution in the reaction vessel. 2-7.(canceled)
 8. The method of producing nickel powder according to claim1, wherein an amount of the dispersant to be added is controlled tocontrol the number of nickel powder obtained through the formation ofthe precipitate of nickel in the reduction.
 9. The method of producingnickel powder according to claim 8, wherein the dispersant is apolyacrylate and the amount of the dispersant to be added is in anamount of more than 1.0% by weight and 10.0% by weight or less based ona weight of the insoluble solid in the reaction vessel.
 10. The methodof producing nickel powder according to claim 8, wherein the dispersantis a lignosulfonic acid and the amount of the dispersant to be added isin an amount of more than 2.0% by weight and 20.0% by weight or lessbased on a weight of the insoluble solid in the reaction vessel.
 11. Themethod of producing nickel powder according to claim 1, wherein thedispersant is a polyacrylate and the amount of the dispersant to beadded is in an amount of more than 1.0% by weight and 10.0% by weight orless based on a weight of the insoluble solid in the reaction vessel.12. The method of producing nickel powder according to claim 1, whereinthe dispersant is a lignosulfonic acid and the amount of the dispersantto be added is in an amount of more than 2.0% by weight and 20.0% byweight or less based on a weight of the insoluble solid in the reactionvessel.